Planes headed to New York's LaGuardia Airport and Philadelphia International Airport were delayed due to wind and low clouds.Credit: Reuters

A wintry blast of heavy rain, wind and snow across the eastern United States could disrupt plans on Wednesday for millions of people traveling ahead of the Thanksgiving holiday.

No widespread flight cancellations were reported, but planes headed to New York's LaGuardia Airport and Philadelphia International Airport were delayed due to wind and low clouds, according to the FlightAware.com tracking site.

Travel conditions were expected to worsen later in the day, with a combination of wet weather and rapidly falling temperatures resulting in slick roads, said AccuWeather.com meteorologist Bill Deger.

"Travel around some of the big cities by road could be a little tricky if people wait until tonight," Deger said.

Boston, New York and Philadelphia "still have a lot more rain to go as we head through the rest of the day," he added.

Moderate to heavy rain was falling over the Southeast and the mid-Atlantic regions on Wednesday, and light to moderate snow was falling across parts of the Ohio Valley to the lower Great Lakes and northern New England, the National Weather Service said.

The National Weather Service said more than 1 foot of snow could fall in western Pennsylvania, western New York and Vermont before skies clear on Thursday.

Flood watches were in effect for eastern portions of the Northeast United States.

The Thanksgiving holiday is one of the nation's busiest travel times, with 43 million Americans expected to make trips this weekend, travel group AAA said.

Thirty-seven percent of travelers will leave on Wednesday, making it the busiest single day of travel for the holiday, AAA said.

For Thanksgiving Day, winds of 15 to 25 miles per hour and gusts even higher are forecast for the Northeast, said Bruce Terry, lead forecaster with the National Weather Service, adding that temperatures were expected to be below freezing.

"We've got everything with this: real heavy rains, (at) the lower elevations a band of freezing rain, heavy snows and then behind it, wind," he said.

The giant character balloons in the Macy's Thanksgiving Day Parade in New York may be grounded if the winds are too strong. City regulations bar the huge balloons from flying when sustained winds top 23 miles per hour, and gusts exceed 34 mph.

New York Gov. Andrew Cuomo issued a winter weather warning and urged motorists to use extreme caution.